The invention is generally related to the field of semiconductor devices and fabrication and more specifically to a method for forming copper lines in integrated circuits using a cap layer process.
To increase the operating speed, high performance integrated circuits use copper interconnect technology along with low dielectric constant (low k) dielectrics. Currently the damascene method is the most widely used method for forming copper interconnects. In a single damascene trench process, the IMD (Intra-Metal Dielectric) is deposited first. The IMD is then patterned and etched to form trenches for the interconnect lines. A barrier layer and a copper seed layer are then deposited over the structure. The barrier layer is typically tantalum nitride or some other binary transition metal nitride. The copper layer is electrochemically deposited (ECD) using the seed layer over the entire structure. The copper is then chemically-mechanically polished (CMP""d) to remove the excess copper from the surface of the dielectric. The single damascene copper via formation in the ILD (Inter-Level Dielectric) can be accomplished in a similar way. In a via-first dual damascene process, an ILD layer is deposited first, followed by an IMD deposition. An IMD etch-stop layer, such as SiN or SiC, can be optionally used in between ILD and IMD. A via is patterned and etched through the IMD and ILD for connection to lower interconnect levels. Then a trench is patterned and etched in the IMD. The barrier layer, copper seed layer and thick copper layer are then deposited over the entire structure. CMP is used to remove the copper from over the IMD, leaving copper interconnect lines and vias.
During the damascene process a number of photolithograph, etch, and clean-up processes are used. Using the low k dielectric films, a number of unwanted interactions occur between these films and the photolithograph, etch, and clean-up processes. The dry etching of the low k dielectrics, such as organosilicate glass (OSG), often has poor selectivity to photoresist. The selectivity is worsened when 193 nm photoresist is used for patterning smaller vias or trenches. Resist erosion during etch can lead to trench and via flaring, and pitting of the dielectric surface. The severity of the problem increases during etch-stop etch and pre-sputter etch when no mask is present to protect the dielectric layer. Severe trench and via flaring, and pitting can result in metal shorts. Various methods have been utilized to try and reduce these interactions including the use of silicon nitride and silicon carbide hardmasks. A major limitation restricting the use of these various hardmasks is the low etch rate selectivity between the low k dielectric layers and these hardmask layers. Typical etch rate selectivity is in the range of xcx9c1:3 to 1:8. There is therefore a need for an improved methodology for forming copper interconnects in integrated circuits, specifically the hardmask selection.
The present invention describes a damascene process for forming integrated circuit interconnects. In particular a Ti(1-x)AlxN capping layer is formed over a low dielectric constant dielectric layer. A trench is formed in the dielectric layer using the capping layer as a hardmask. Copper is then used to fill the trench thereby forming the integrated circuit interconnect.
In another embodiment of the invention, first and second trenches are formed in the dielectric layer. The second trench is positioned above the first trench. The capping layer is used as a hardmask for the formation of both the first and second trench. Copper is then used to form a contiguous layer in both the first and second trench.